Ceramic capacitors use ceramic materials such as titanium oxide and barium titanate as dielectric members. In characteristics screening tests for quality assurance of products like above ceramic capacitors, ceramic capacitors are charged with a DC voltage and are then discharged. The test includes an insulation resistance test and a breakdown voltage test. The ceramic capacitors, however, are not fully discharged, and some electric charge is trapped and remains inside due to polarization.
Polarization is described below. In a ceramic capacitor, as it uses ceramic material as a dielectric member, dielectric particles in it respectively form electric dipoles each having a positive pole and a negative pole. Before application of a DC voltage, the electric dipoles can rotate freely each other, and are thus electrically neutralized. Thus, the ceramic capacitor has a required amount of capacitance. When a DC voltage is applied during the screening tests mentioned above, the internal electric dipoles are aligned so that the negative poles face a positively charged electrode of the ceramic capacitor whereas the positive poles face a negatively charged electrode. Accordingly, in the ceramic capacitor after the application of a DC voltage, the electric dipoles are aligned so as to inhibit flow of current; that is, capacitance is reduced.
A ceramic capacitor that reduces capacitance may not be used as a product. Thus, to recover capacitance of the ceramic capacitor, the ceramic capacitor having reduced capacitance generally undergoes an annealing process after the insulation resistance test. In this process the ceramic capacitor is heated to a temperature at or above the Curie point, (the temperature at which the polarization disappears) of the internal dielectric member and is maintained at that temperature for a required period of time. Accordingly, in the ceramic capacitor, the aligned electric dipoles of the dielectric member are freed, allowing the electric dipoles to freely rotate each other, whereby the capacitance of the ceramic capacitor is recovered.
The annealing process described above takes a long time because the ceramic capacitor must be heated to a high temperature. Thus, in order to increase production capacity, ceramic capacitors are manufactured by a batch process; that is, a plurality of ceramic capacitors is processed simultaneously instead of every one capacitor is processed one by one.
In the batch process, a large number of ceramic capacitors are mounted on a metallic tray, and the annealing process is performed. When the ceramic capacitors are picked off the tray, they adhere to the surface of the tray due to the high-temperature at the annealing time, making it more difficult to pick them off. Even if the ceramic capacitors are picked off, the adhesion of components of the ceramic capacitors requires time to be spent cleaning the tray, and the like, resulting in a lowering of production efficiency.
Furthermore, as part of the annealing process, performed after the tests in the ceramic capacitor manufacturing process time is required to cool the capacitors as they are heated to a high temperature. As a result, the annealing process must be performed separately from a packing product process after manufacturing, such as taping or bulk packing.
Because the annealing and packing processes are performed separately as described above, the cost of manufacturing ceramic capacitors is higher at least for the increased amount of work. Furthermore, longer time is required for a single annealing process, resulting in reduction of production capacity.